The research described in this proposal is designed to develop a mathematical model that will enable the industrial hygiene engineer to make reliable estimates of personal exposure to individuals who are working at operations under the control of local exhaust hoods. The proposal focuses on the importance of the worker as an obstruction in the flow field of the hood, and how the phenomenon of boundary layer separation influences exposure. The long range objective is the development of optimal hood designs through an understanding of the factors that impact on the hood's ability to control exposure. The term optimal refers to achieving a desired level of control at the lowest cost. Specific Aims include the development of personal exposure models for uniform flows such as would be found in spray booths, and also exposure vs. capture efficiency models for flanged circular hoods. The effect of crossdrafts and the position of the worker on exposure will also be examined.